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Installation

Electrical

Installation

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Started

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parameters

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the motor

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operation

PC tools

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parameters

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UL Listing

Information

Affinity User Guide

223

Issue Number: 5 www.controltechniques.com

The following table shows the voltage levels used by drives with each
voltage rating.

* Vml

is defined by Pr

6.48

. The values in the table above are the

default values.

The line power supply loss detection level can be adjusted using this
parameter. If the value is reduced below the default value, the default
value is used by the drive. If the level is set too high, so that the line
power supply loss detection becomes active under normal operating
conditions, the motor will coast to a stop.

Open-loop

These parameters control the proportional and integral gains of the
current controller used in the open loop drive. As already mentioned the
current controller either provides current limits or closed loop torque
control by modifying the drive output frequency. The control loop is also
used in its torque mode during line power supply loss, or when the
controlled mode standard ramp is active and the drive is decelerating, to
regulate the flow of current into the drive. Although the default settings
have been chosen to give suitable gains for less demanding applications
it may be necessary for the user to adjust the performance of the
controller. The following is a guide to setting the gains for different
applications.

Current limit operation:

The current limits will normally operate with an integral term only,
particularly below the point where field weakening begins. The
proportional term is inherent in the loop. The integral term must be
increased enough to counter the effect of the ramp which is still
active even in current limit. For example, if the drive is operating at
constant frequency and is overloaded the current limit system will try
to reduce the output frequency to reduce the load. At the same time
the ramp will try to increase the frequency back up to the demand
level. If the integral gain is increased too far the first signs of

instability will occur when operating around the point where field
weakening begins. These oscillations can be reduced by increasing
the proportional gain. A system has been included to prevent
regulation because of the opposite actions of the ramps and the
current limit. This can reduce the actual level that the current limit
becomes active by 12.5%. This still allows the current to increase up
to the current limit set by the user. However the current limit flag
(Pr

10.09

) could become active up to 12.5% below the current limit

depending on the ramp rate used.

Torque control:

Again the controller will normally operate with an integral term only,
particularly below the point where field weakening begins. The first
signs of instability will appear around base speed, and can be
reduced by increasing the proportional gain. The controller can be
less stable in torque control mode rather than when it is used for
current limiting. This is because load helps to stabilise the controller,
and under torque control the drive may operate with light load.
Under current limit the drive is often under heavy load unless the
current limits are set at a low level.

Line power supply loss and controlled standard ramp:

The DC bus voltage controller becomes active if line power supply
loss detection is enabled and the drive supply is lost or controlled
standard ramp is being used and the machine is regenerating. The
DC bus controller attempts to hold the DC bus voltage at a fixed
level by controlling the flow of current from the drive inverter into its
DC bus capacitors.
The output of the DC bus controller is a current demand which is fed
into the current PI controller as shown in the following diagram.

Although it is not usually necessary the DC bus voltage controller
can be adjusted with Pr

5.31

. However, it may often be necessary to

adjust the current controller gains to obtain the required
performance. If the gains are not suitable it is best to set up the drive
in torque control first. Set the gains to a value that does not cause
instability around the point at which field weakening occurs. Then
revert back to open loop speed control in standard ramp mode. To
test the controller the supply should be removed while the motor is
running. It is likely that the gains can be increased further if required
because the DC bus voltage controller has a stabilising effect,
provided that the drive is not required to operate in torque control
mode.

RFC

The Kp and Ki gains are used in the voltage based current controller.
The default values give satisfactory operation with most motors.
However it may be necessary to change the gains to improve the
performance. The proportional gain (Pr

4.13

) is the most critical value in

controlling the performance. Either the value can be set by auto-tuning
(see Pr

5.12

) or it can be set by the user so that

4.13

= Kp = (L / T) x (I

/ V

) x (256 / 5)

Where:

T is the sample time of the current controllers. The drive
compensates for any change of sample time, and so it should be
assumed that the sample time is equivalent to the lowest sample
rate of 167

L is the motor inductance. For an induction motor this is the per
phase transient inductance (

). This is the inductance value stored

in Pr

5.24

after the autotune test is carried out.

Voltage level

200V drive

400V drive

575V drive

690V drive

Vuu

175